This invention relates to a method and apparatus for monitoring X-ray radiation, and more particularly to a method and apparatus for monitoring X-ray radiation in a CT X-ray tube housing.
As is well known, X-ray tubes are currently used in various medical equipment for making X-ray images of patients. The X-ray images are then used for various diagnostic functions. An X-ray tube gives off a beam of X-ray radiation. Part of this X-ray radiation is absorbed by the body and part of the X-ray radiation radiates through the body. To make an X-ray image, a piece of X-ray film is placed behind the body and an X-ray tube is aimed at the front of the body. When the tube generates X-ray energy, a shadow graph appears on the developed film.
Another type of X-ray tube is a CT X-ray tube which is used in CT (Computerized Tomography) scan machines. This tube puts out a planar beam which is then rotated around the body during operation. Various sensors are located around the body to detect the intensity of the beam. The sensors are connected to a computer which generates an image of a slice of the body. The CT X-ray tube is then moved longitudinally along the body sequentially generating slices so that the computer can generate a three-dimensional image of the body.
CT X-ray tubes are relatively expensive and therefore, it is desirable that tube manufacturers have a way of monitoring the total tube operation time for warranty purposes. For institutions such as hospitals to be able to afford such equipment, the CT scan machine must be run continuously. This constant operation causes the CT X-ray tube to become hot. Further, the high temperatures within the CT X-ray tube result in gases being given off within the X-ray tube housing which limit the life expectancy of a CT X-ray tube. Due to a CT X-ray tube's limited life expectancy, both the number of exposures and time of each exposure may need to be monitored to measure the tube's total time of operation. The monitored measurements can then be used to calculate tube warranties.
Further, it is desirable to get status information about the environment of the X-ray tube during operation. This information which includes the exposure time, the housing temperature and exposure rate can be used in a reliability analysis. This analysis can be used to predict the number of exposures before tube failure. Further analysis can then be done to examine the effect of median exposure time and housing temperature on the X-ray tube's reliability.
Two prior ways in which X-ray tubes are monitored are as follows. First, a counter is connected to the power switch in the CT scan machine so that the count is incremented by one each time the tube is activated. Accordingly, the counter keeps track of the number of cycles of the X-ray tube. This method of exposure count monitoring is inaccurate because CT X-ray tubes are interchangeable and can be easily switched in and out of the CT scan machine. For example, when a second tube is swapped in for a first tube, the exposure count is inaccurate, as it would be indeterminate whether the count is for the first or second tube. Further, a power switch counter has further deficiencies as it is not able to record the temperatures within the CT X-ray tube housing. Also, current power switch counters do not indicate the length of an CT X-ray tube exposure.
A second method of monitoring the exposure of an X-ray tube involves the use of exposure equipment that measures X-ray radiation. This exposure equipment is placed in the front of the X-ray tube and monitors the exposure time and the power of each cycle. However, this piece of test equipment is not physically tied to any CT X-ray tube. Accordingly, CT X-ray tubes can still be swapped in and out of the CT scan machine, thereby giving an inaccurate reading of the life cycle for the CT X-ray tube presently in the CT scan machine. This second method requires human intervention to accurately record the X-ray tube cycles which can result in inaccuracies in the life cycle data.